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contaminated gas driving me crazy

guys,
while tig welding aluminum at work on our 250 syncrowave, lately i am getting a lot of bad cylinders of gas, 75/25- argon helium.
this is confirmed by me once i get a suspected bad cylinder, i hook up the previous, almost empty bottle, and everything runs fine.
when welding with the bad gas, i get a very erratic arc, both before and after adding filler, and it is very hard to achieve a nice appearing bead. the arc is so unstable you can actually hear the difference, and the etching / cleaning zone is like twice the size with the bad gas, compared to the good gas.

after switching out cylinder the past couple of weeks, our supplier, airgas, took one of the bottles i said was bad, had its contents analyzed, and sure enough it had nitrogen and oxygen in it. that made me happy knowing it was bad gas.

but, they said they checked 5-10 other cylinders, these checking out good, put them aside just for me, and yesterday i had 3 of them all act up just as before. again, hooking up the one cylinder that ran good for almost 4 days cured the problem.

i kind of dont want to believe they actually tested the other cylinders they are saying are good, since i wasnt there. i think they are just covering their selves.

i talked to an engineer at a place called nupure, http://nupure.com/, and he said he hears of this problem all the time. he said some traces of nitrogen is normal with argon and helium, but said there should be absolutely no traces of oxygen. they do make two different styles of gas purifiers, but they are very pricey at 2-3k....

just curious if you guys have had multiple bottles of bad argon, argon/helium in the past ? how many did you have in a row that were bad ? i searched the internet and found multiple stories of bad gas.

also, some time ago, someone told me to get a clean piece of steel, stike and arc at low amps, keep the torch there until the gas stops purging, and i think he said if it shows a dirty, discolored area in or around the solidified puddle, it means contaminated gas, if it looks all clean the gas is good.

I had a problem welding aluminum with a new cylinder once.. i actually thought it was a bad piece of aluminum. It would go erratic when i added the filler. Make a long story short, i tried cleaning the material and my filler and it worked sometimes. Come to find out it was something blocking my regulator.. there was something in the new cylinder and it went in the regulator. I would try turning your gas way up and see if it still does it

LOL...
thanks guys, i have even tried swapping to another regulator, and a new torch, with no cure.... to me i know it has to be the gas, if i can swap back to the good bottle that gave absolutely no problems for 4 days and it then will run fine..
anymore stories of bad agon, argon / helium ?

Maybe they gave you some 75/25 helium /argon....that would account for a jumpy,erratic arc.

thanks, but it is 75/25 argon helium.
its now acting even stranger. today i welded first thing this morning and it was 90% normal for about 15 minutes. as time went on it got worse and around the 4th hours it was just about unbearable. stopped welding for about 2 hours, to do other things, came back and it was then running close to what im use to, for the last hour of work before i went home.
i will find out how it goes tomorrow.
when its acting up the arc is really erratic and i can not get a ripply bead and the cleaning/etching zone is more than twice the width it normally is when its running fine because of the arc jumping all around.
i will let you know how tomorrow goes... from past experience, sooner or later i will get some bottles that are an absolute joy to weld with, and when i get a bottle like that, im gonna really raise some cane with the supplier.

I don't know what it would be but the progressive nature of the problem makes me wonder if it is not something with the machine rather than the gas. Something heating up and changing the output or constricting/contaminating the gas flow? Do you have another machine that you could try the gas on?---Meltedmetal

well guys, so far it seems i found the problem. im 99% sure its fixed and will confirm it with more welding next week.

it seems that different cylinders of the 75/25 argon helium sometimes like different CFH flow rates.

i was switching back and forth today with 3 bottles and 2 acted pretty much the same, and one didnt want to weld at all, all erratic.

i am a creature of habit and like to keep everything the same, and always keep my flow rate at 25CFH, but that one bottle liked it at 15CFH....

im guessing that if the bottle contents are not the same, thats the reason for the need of varying flow rates. i can now, with any of the three bottle i have, make any of then act up or run perfect, just by adjusting the flow rate

like i said, i will see how it goes next week.... all the searching i did, talking with an engineer from nupure, talking with miller and e-mailing other guys, could not figure it out.
im just happy i can now weld the thick aluminum with no problems and get back on schedule. it really was driving me crazy.
thanks guys for the input